Vacuum cleaners are generally supplied with a range of tools for dealing with specific types of cleaning. The tools include a floor tool for general on-the-floor cleaning. It is well-known to provide a floor tool in which a brush bar is rotatably mounted within a suction opening on the underside of the tool, with the brush bar being driven by an air turbine. The brush bar serves to agitate the floor surface beneath the tool so as to release dirt, dust, hair, fluff and other debris from the floor surface where it can then be carried by the flow of air to the vacuum cleaner itself. The turbine can be driven solely by ‘dirty’ air which enters the tool via the suction opening, it can be driven solely by ‘clean’ air which enters the tool via a dedicated inlet which is separate from the main suction opening, or it can be driven by a combination of dirty and clean air. ‘Dirty air’ turbine-driven tools have a disadvantage in that they can easily become fouled by the dirty airflow. They also have a disadvantage in that the speed at which the turbine rotates can increase quite rapidly when the tool is lifted from a surface.
U.S. Pat. No. 5,950,275 and DE 42 29 030 both show dirty air turbine-driven tools where a speed limiting function is operable when the tool is lifted from a surface. In one of the tools, the speed limiting device is a floor engaging wheel which controls the angular position of an air inlet with respect to the turbine.
‘Clean air’ turbine-driven tools can also suffer from an increase in speed under certain conditions. A full or partial blockage of the airflow path through the main suction inlet to the tool can cause an increased amount of air to flow through the air turbine inlet, which increases the speed of the turbine and the brush bar. However, in view of the different causes of an overspeed condition in clean air and dirty air turbine-driven tools, the solutions proposed for dirty air turbine-driven tools are unsuitable for use in clean air turbine-driven tools.